Notes

The Fast Nationals rating and share are released one to two days following the airing of an episode. The information mainly comes from electronic methods of data collection (i.e. DVR and Nielsen boxes).

The final Nielsen rating and share is released the following week after a program airs, and includes additional slower-to-process data including from non-electronic data collection methods such as mail-in and website submitted surveys. The above tables log the final Nielsen results for households with members aged 18-49.

The final Nielsen ratings in the above tables are also known as the Live+Same Day ratings because all of the data is related to viewing that occurred on the date of original broadcast. Nielsen also releases Live+7 Day ratings two weeks after the date of original broadcast. These ratings include delayed viewership results from Tivo and other methods up to one week after the original broadcast. Heroes's Live+7 Day ratings have been as much as 20% higher than Live+Same Day in Season 3, and NBC uses these results for its own TAMi ratings system.

The rating, whether Fast Nationals or final Nielsen, refers to the percentage of total USA households who watched the program. Share is a similar percentage, but is restricted to those households who were actually watching TV. Thus, the share is usually greater than the rating and can never be less than the rating.

Sources

Fast Nationals rating and share are available one to two days after airing from Zap2It.com (rating/share is specified next to the program name).

18–49-year-old rating and share (final Nielsen version) are published on the pifeedback.com forum by the following week.

18–49-year-old viewers is published at tvbythenumbers.com the following week as well.